1. Field of the Invention
The present invention relates to a marine gas cylinder apparatus.
2. Description of the Related Art
Conventionally, as described in Japanese Patent Application Publication No. 7-81682 (patent publication 1), a marine gas cylinder apparatus includes a structure in which a cylinder block is connected to one of either a hull or a propulsion unit. A piston rod inserted into the cylinder block from a rod guide provided in the cylinder block is connected to the corresponding hull or propulsion unit. A piston rod side oil chamber in a side which receives the piston rod and a piston side oil chamber in a side which does not receive the piston rod are provided within the cylinder block. High pressure gas is charged into a portion above a working fluid in the piston rod side oil chamber, and a switching valve apparatus capable of switching a communication state among the piston rod side oil chamber and the piston side oil chamber is provided in the cylinder block. It is possible to manually tilt up and down the propulsion unit easily while obtaining an assist force applying a gas pressure to the piston rod, by communicating the piston rod side oil chamber and the piston side oil chamber, on the basis of an opening operation of the switching valve apparatus.
In the prior art in the patent publication 1, since a gas chamber is provided in an inner portion of the piston rod side oil chamber, it is impossible to lock movement of the piston even by shutting off the communication between the piston rod side oil chamber and the piston side oil chamber on the basis of a closing operation of the switching valve apparatus, so that it is impossible to make the propulsion unit in a tilt-lock state at an optional position.
Accordingly, the applicant of the present invention proposes a switching valve apparatus of a marine gas cylinder apparatus as set out in Japanese Patent Application No. 2002-84246. This switching valve apparatus of the marine gas cylinder apparatus comprises a check valve which is provided in a communication passage communicating a piston rod side oil chamber with a communication chamber and is opened by pressure of the piston rod side oil chamber. A check valve is also provided in a communication passage communicating the piston side oil chamber with the communication chamber which is opened by pressure of the piston side oil chamber, and a check valve provided in a communication passage communicating the gas chamber with the communication chamber and which is opened by pressure of the gas chamber. In accordance with this structure, it is possible to simultaneously open and close all the check valves. It is possible to communicate all the communication passages with each other in the communication chamber by opening all the check valves on the basis of the opening operation. It is possible to easily manually tilt the propulsion unit up and down while obtaining an assist force applying the gas pressure of the gas chamber to the piston rod. Further, it is possible to shut off all the communication passages with respect to the communication chamber by closing all the check valves during a closing operation so as to prevent the influence of the gas chamber from being applied to the piston rod side oil chamber and the piston side oil chamber. It is thereby possible to lock the movement of the piston and it is possible to tilt-lock the propulsion unit at optional positions.
However, in the gas cylinder apparatus mentioned above which the applicant of the present invention proposes, the communication chamber becomes a sealed space by the closing operation of the switching valve apparatus. That is, each of the check valves comprising the switching valve apparatus is operated by a spring force and a pressure difference. It is structured such that if any check valve is opened by the pressure of the communication passage in any of the piston rod side oil chambers, the piston side oil chamber and the gas chamber, the other check valves are closed by the pressure (the back pressure) of the communication chamber, and the opened check valve is again closed, so that the communication chamber forms a sealed space. As described above, since the communication chamber of the switching valve apparatus forms the sealed space, the hydraulic pressure of the communication chamber becomes excessively high at a time when the working fluid in the communication chamber is expanded due to the abnormal temperature increase. Therefore, a heavy load is required for opening the check valve, and there is a risk that the switching valve apparatus becomes broken.